1. Technical Field of the Invention
The present invention relates to a wheel identifying apparatus for use in a vehicle, which has an improved mounting structure of triggering devices for ensuring the accuracy of wheel identification of the apparatus.
2. Description of the Related Art
A direct-type tire inflation pressure detecting apparatus generally includes a plurality of transmitters (or transceivers) and a receiver.
Each of the transmitters is directly mounted on one of a plurality of wheels of a vehicle and includes a pressure sensor for sensing the inflation pressure of a tire fitted on the wheel. Each of the transmitters is configured to transmit a pressure signal representative of the inflation pressure of the tire sensed by the pressure sensor.
The receiver is mounted on the body of the vehicle and includes at least one antenna. The receiver is configured to receive, via the antenna, the pressure signals transmitted from the transmitters and determine the inflation pressures of the tires based on the received pressure signals.
In the above apparatus, the receiver may also receive pressure signals transmitted by external transmitters (e.g., transmitters mounted on wheels of other vehicles). However, it is impossible for the receiver to determine whether a pressure signal received thereby has been transmitted by one of the transmitters of the apparatus or by an external transmitter. Moreover, it is also impossible for the receiver to detect the locations of the transmitters on the vehicle. In other words, the receiver cannot identify the wheel on which the transmitter having transmitted a pressure signal and the tire whose inflation pressure is indicated by the pressure signal are located.
To solve the above problems, as disclosed in U.S. Pat. No. 5,602,524, each of the transmitters may be further configured to transmit an identification signal (to be referred to as ID signal hereinafter) representative of the identity thereof along with the pressure signal. On the other hand, the receiver may be further configured to have reference ID signals registered therein, each of which coincides with the ID signal of one of the transmitters and is associated with the location of that transmitter.
Thus, the receiver may compare an ID signal received thereby with the reference ID signals registered therein and identify the transmitter which has transmitted the ID signal when the ID signal coincides with one of the reference ID signals.
Consequently, the receiver can identify the wheel on which the identified transmitter is mounted. More specifically, the receiver can determine whether the wheel is a FR (front-right), a FL (front-left), a KR (rear-right), or a RL (rear-left) wheel of the vehicle. Further, the receiver can determine the inflation pressure of the tire fitted on the identified wheel based on the pressure signal received along with the ID signal.
However, with the above configuration, it is required to previously register the ID signals specific to the respective transmitters as reference ID signals in the receiver through associating the ID signals with the locations of the respective transmitters on the vehicle (i.e., the wheels on which the respective transmitters are mounted). Moreover, as tire replacement or rotations are performed, it is required to update the reference ID signals in the receiver.
However, the registration of the ID signals in the receiver is a time-consuming task, and thus it is desired to automatically perform the registration task. Further, for automatically performing the registration task, it is desired to automatically detect the locations of the transmitters (or the associated tires), in other words, to automatically identify the wheel on which each of the transmitters (or the associated tires) is located.
To meet the above desires, US Patent Application Publication No. 2007/0008097 A1 discloses a wheel identifying apparatus. This apparatus includes a plurality of transceivers, each of which is located on one of a plurality of wheels of a vehicle, at least one triggering device that is mounted on the body of the vehicle at different distances from the transceivers, and a receiver located on the body of the vehicle. The triggering device transmits a trigger signal whose strength attenuates with increase in the distance from the triggering device. Therefore, the strengths of the trigger signal at the transceivers are different from each other. In response to receipt of the trigger signal, each of the transceivers determines the strength of the trigger signal thereat and transmits a response signal which conveys signal strength information on the determined strength of the trigger signal. The receiver receives the response signals transmitted by the transceivers and identifies, for each of the received response signals, the wheel on which the transceiver having transmitted the response signal is located based on the signal strength information conveyed by the response signal.
Further, as an application to a four-wheel vehicle, the wheel identification apparatus includes a first triggering device and a second triggering device. The first triggering device is mounted on the body of the vehicle closer to the front axle of the vehicle than the rear axle, so that a first trigger signal transmitted by the first triggering device can be received only by the transceivers located on the front wheels (i.e., the FR and FL wheels). Further, the first triggering device is mounted at different distances from the front wheels, so that strengths of the first trigger signal at the transceivers on the front wheels are different from each other. Thus, the receiver can identify, for each of the transceivers on the front wheels, the wheel on which the transceiver is located based on the strength of the first trigger signal at the transceiver. On the other hand, the second triggering device is mounted on the body of the vehicle closer to the rear axle of the vehicle than the front axle, so that a second trigger signal transmitted by the second triggering device can be received only by the transceivers located on the rear wheels (i.e., RR and RL wheels). Further, the second triggering device is mounted at different distances from the rear wheels, so that strengths of the second trigger signal at the transceivers on the rear wheels are different from each other. Thus, the receiver can identify, for each of the transceivers on the rear wheels, the wheel on which the transceiver is located based on the strength of the second trigger signal at the transceiver.
With the above configuration, for ensuring the accuracy of wheel identification of the apparatus, it is essential that the first trigger signal transmitted by the first triggering device can be reliably received by both the transceivers on the front wheels, and the second trigger signal transmitted by the second triggering device can be reliably received by both the transceivers on the rear wheels.
To this end, one may consider increasing the transmitting strengths at which the first and second triggering devices transmit the respective first and second trigger signals. However, with the increased transmitting strengths, the first trigger signal may be unwantedly received by either or both of the transceivers on the rear wheels, and the second trigger signal may be unwantedly received by either or both of the transceivers on the front wheels. Moreover, the transmitting strengths of the first and second trigger signals are usually restricted under regulations. Therefore, there is a limitation in increasing the transmitting strengths of the first and second trigger signals.
Furthermore, there exist several factors attenuating the first and second trigger signals, such as the relatively long distances between the first triggering device and the farther one of the transceivers on the front wheels and between the second triggering device and the farther one of the transceivers on the rear wheels, which generally correspond to the length of the front and rear axles of the vehicle, and metal structures existing in the transmission paths of the first and second trigger signals. Therefore, when the first and second triggering devices are not suitably mounted on the body of the vehicle, it will be difficult to ensure that the first trigger signal is reliably received by both the transceivers on the front wheels and the second trigger signal is reliably received by both the transceivers on the rear wheels.